Understanding dietary behavior can become a complex endeavor. Population-level nutritional assessments offer beneficial insights into nutritional patterns and behavior; however, they often rely on survey-based methods subject to recall bias. While informative, these limitations may impede overall progress on forming links between diet and associated health outcomes, such as obesity or impacts of food insecurity, warranting alternative techniques. Wastewater-based epidemiology (WBE) offers a unique perspective on population-level human behavior, activity, and exposure and has been proposed as a viable tool for dietary assessment due to its inclusive, cost-effective, and near real-time capabilities. Thus, the work presented here tests this application of WBE in a two-year case study (August 2017 through July 2019) integrating a multidisciplinary approach to (i) investigate trends of indicators of phytoestrogens, representing a plant-based diet, (ii) evaluate novel parent-metabolite relationships, and (iii) assess feasibility of analyzing human gut bacteria at the population-level. Twenty-four-hour composite samples were collected from within a sub-catchment of a southwestern U.S. city for seven consecutive days each month (n = 156) and analyzed for indicators of two major classes of phytoestrogens (isoflavones and lignans). Results of the chemical analysis exhibit distinct trends (mg-d^-1 per capita), with statistically significant seasonal changes (p ≤ 0.01), and a strong positive correlation between parent compound daidzein and microbial metabolite, equol (ρ = 0.84). 16S rRNA gene amplicon sequencing of a subset of community wastewater samples revealed human gut bacterial genera involved in phytoestrogen metabolism were measurable at population-scale, potentially offering deeper insights into linkages between diet, the human microbiome, and health outcomes. This study is the first to report such a comprehensive analysis of population-level dietary patterns from a chemical and biological vantage point, and thus, may serve as a foundation for future investigations of utilizing WBE for nutritional assessment to enhance public health nutrition efforts.

Erin Driver

Arizona State University

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